This Conte Center resubmission will use a multi-modal, multi-species approach to investigate the neurobiological underpinnings of social decision-making. Three cores provide administrative, neuroimaging, and participant recruitment and assessment resources for four Projects that are each directed by internationally renowned leaders in social neuroscience and decision neuroscience, all of whom have a track record of scientific collaboration, student training, and expertise in the topic of the planned studies. The Projects constitute a cohesive set of experiments in humans and monkeys that will use the resources of the Caltech Brain Imaging Center for fMRI studies of the brain, existing collaborations with three hospitals for intracranial recordings in neurosurgical patients, together with the resources of labs at Caltech and at Cambridge for electrophysiological recordings in nonhuman primates. Project 1 provides a foundational investigation of basic social reward processing (e.g., representing the value of emotional faces), and how this compares with nonsocial reward processing (e.g., the value of juice). Project 2 investigates how we can learn choices by observing other people's decisions. Project 3 investigates how we can make decisions that are based on another person's value (such as in altruistic behaviors). Project 4 investigates the connectivity of the brain structures revealed by the other Projects to underlie social decision-making, such as the amygdala and parts of the prefrontal cortex. Each Project includes both fMRI and electrophysiology, and studies in both humans and monkeys. This science is woven into a training and outreach program emphasizing dissemination and diversity; and all data are made available for data sharing. The uniform recruitment and assessment of participants, the tight integration and communication between Projects, and the collaborative track record of the team will leverage these studies to a systematic and coordinated investigation of the largest outstanding questions in social decision-making, an enterprise that only a Conte Center mechanism could make possible.